Method for controlling storage system, and storage control apparatus

ABSTRACT

A method for controlling a storage system including a host computer, and a first and a second storage control apparatuses each receiving a data input/output request from the host computer and executing a data input/output process for a storage device in response to the request, comprises connecting a first communication path between the host computer and the first apparatus; connecting a second communication path between the first apparatus and the second apparatus; receiving by the first apparatus a first data input/output request from the host computer through the first path; when the first apparatus has judged that the first request is not for the first apparatus, transmitting by the first apparatus a second data input/output request corresponding to the first request, to the second apparatus through the second path; and by the second apparatus, receiving the second request and executing a data input/output process corresponding to the second request received.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priorities upon Japanese PatentApplication No. 2002-127058 filed on Apr. 26, 2002 and Japanese PatentApplication No. 2002-333540 filed on Nov. 18, 2002, which are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a storagesystem and to a storage control apparatus.

2. Description of the Related Art

In recent years, the environment surrounding information systems israpidly changing such as the progress of information technology (IT) andmeasures for the shift to broadband. Along with this, the rapid increaseof the amount of data handled is a serious problem in various occasions.

To deal with such an increase of the amount of data, storage systemsoperated in data centers are being subjected to larger capacities andhigher performances of the storage control apparatuses such as diskarray units. Therefore, for example, in data centers, introductions ofand replacements with storage control apparatuses having higherperformances and larger capacities are frequently carried out in orderto respond to the rapid shift to larger capacities of storage controlapparatuses.

There are methods for introducing a storage control apparatus, such asthe ones in which the operation using the old storage controlapparatuses has been completely shifted to the operation using only thenewly introduced storage control apparatuses, and the ones in which theoperation is carried out where the old storage control apparatusescoexist with the newly introduced storage control apparatuses.

As one of the former methods, there is a technology described inJapanese Patent Application Laid-open (Kokai) Publication No. Hei10-508967. In this method, all the data can be operated by the newstorage control apparatuses having a higher performance and a largercapacity, however, effective use of the old storage control apparatusescannot be facilitated.

On the other hand, in one of the latter methods, the effective use ofthe old storage control apparatuses can be facilitated. However, thenumber of the storage control apparatuses directly connected to networksbecomes necessarily increased because both of the new and the oldstorage control apparatuses coexist, and network structure informationmust be re-constructed because the new storage control apparatuses havebeen introduced to the existing networks. Therefore, an increase inmanagement load imposed by the shift and the operation is inevitable.

SUMMARY OF THE INVENTION

One object of the invention is to facilitate effective use of oldstorage control apparatuses when, for example, introducing new storagecontrol apparatuses to an existing storage system.

Another object of the invention is to facilitate the use of old storagecontrol apparatuses without increasing the management load of thestorage system after introducing new storage control apparatuses. Yetanother object of the invention is, in that situation, to makespecification changes and modifications to the old storage controlapparatuses unnecessary or minimal.

Further object of the invention is to enable the use of storage controlapparatuses designed for being used directly connected to a hostcomputer without any modification or with minimal necessaryspecification changes not only when introducing new storage controlapparatuses to an existing storage system but also when operating astorage control apparatus which is connected to another storage controlapparatus.

In order to achieve the above and other objects, an aspect of theinvention provides a method for controlling a storage system including ahost computer, and a first and a second storage control apparatuses eachhaving a function for receiving a data input/output request transmittedfrom the host computer and executing a data input/output process for astorage device in response to the data input/output request received,comprising:

-   -   connecting a first communication path between the host computer        and the first storage control apparatus to each other;    -   connecting a second communication path between the first storage        control apparatus and the second storage control apparatus to        each other;    -   receiving by the first storage control apparatus a first data        input/output request transmitted from the host computer through        the first communication path;    -   when the first storage control apparatus has judged that the        first data input/output request is not to be handled by the        first storage control apparatus, transmitting by the first        storage control apparatus a second data input/output request        corresponding to the first data input/output request, to the        second storage control apparatus through the second        communication path; and    -   by the second storage control apparatus, receiving the second        data input/output request and executing a data input/output        process corresponding to the second data input/output request        received.

Features and objects of the present invention other than the above willbecome clear by reading the description of the present specificationwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings wherein:

FIG. 1 shows the structure of a storage system according to oneembodiment of the invention;

FIG. 2 shows a structure information management table according to oneembodiment of the invention;

FIG. 3 shows a data format of a data input/output request transmittedfrom a host computer to a first storage control apparatus, according toone embodiment of the invention;

FIG. 4 illustrates processes of the storage system according to oneembodiment of the invention when the data input/output requesttransmitted from the host computer is a data write-in request;

FIG. 5A and FIG. 5B respectively illustrates a concept of access limitprocess according to one embodiment of the invention;

FIG. 6 illustrates processes of a storage system concerning its datacopy function, according to one embodiment of the invention;

FIG. 7 illustrates a snapshot function according to one embodiment ofthe invention;

FIG. 8 illustrates a snapshot function according to one embodiment ofthe invention;

FIG. 9 illustrates a mechanism for reflecting new data on a first logicvolume, according to one embodiment of the invention;

FIG. 10 illustrates a mechanism for reflecting the new data on the firstlogic volume, according to one embodiment of the invention;

FIG. 11 illustrates a mechanism for reflecting the new data on the firstlogic volume, according to one embodiment of the invention;

FIG. 12 shows a table for managing flags being related to cacheaddresses designating storage positions of the new data on a cachememory, according to one embodiment of the invention;

FIG. 13 shows a table for managing the remaining amount of the cachememory, according to one embodiment of the invention;

FIG. 14 illustrates a situation where the first logic volume is set as acopy source and a second logic volume is set as a copy destination,according to one embodiment of the invention;

FIG. 15 illustrates a situation where the first logic volume is set asthe copy destination and the second logic volume is set as the copysource, according to one embodiment of the invention;

FIG. 16 illustrates a situation where the first logic volume is used forstoring old data and the second logic volume is used for storing newdata, according to one embodiment of the invention;

FIG. 17 illustrates a situation where the first logic volume is used forstoring the new data and the second logic volume is used for storing theold data, according to one embodiment of the invention;

FIG. 18 illustrates a process concerning check codes, according to oneembodiment of the invention;

FIG. 19 shows a hardware structure of the first storage controlapparatus and the second storage control apparatus, according to oneembodiment of the invention;

FIG. 20 shows the main functional blocks included in the first storagecontrol apparatus and the second storage control apparatus, according toone embodiment of the invention;

FIG. 21 illustrates a situation where an LUN of the second storagecontrol apparatus is managed being mapped on the first storage controlapparatus side, according to one embodiment of the invention;

FIG. 22 illustrates an operation of the storage system when a datainput/output request in which a special reservation command directed toa storage device of the second storage control apparatus is described istransmitted from the host computer to the first storage controlapparatus, according to one embodiment of the invention;

FIG. 23 shows an LU map information table, according to one embodimentof the invention;

FIG. 24 shows a reservation information table according to oneembodiment of the invention;

FIG. 25 illustrates an operation of the storage system according to oneembodiment of the invention when an E-copy command instructing to copydata in the second logic volume of the second storage control apparatusto a back-up device connected to a third storage control apparatus istransmitted from a host computer to the first storage control apparatus;and

FIG. 26 shows a flowchart illustrating processes executed by the firststorage control apparatus, according to one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At least the following facts will be revealed by the description hereinand the illustration of the accompanying drawings.

<Overview of Disclosure>

In the above invention, each of the first and the second storage controlapparatuses is, for example, a storage apparatus provided to a user asone product such as a disk array apparatus. More specifically, the firststorage control apparatus has a communication interface for connectingit to the first and the second communication means, a CPU for executinga data input/output process for a disk drive in response to the firstdata input/output request and a cache memory for storing data inputto/output from the disk drive during the data input/output process.

The second storage control apparatus has a communication interface forconnecting it to the second communication means, a CPU for executing adata input/output process for the storage device in response to thesecond data input/output request and a cache memory for storing datainput to/output from the disk drive during the data input/outputprocess.

Each of the first and the second storage control apparatuses operates asone single disk array apparatus when they are introduced to a networksuch as, for example, SAN, and can respectively receive as one singleapparatus the data input/output request transmitted from the hostcomputer and can execute a data input/output process in response to thedata input/output request, to a storage device such as an integrated orexternally-connected disk drive.

In the above structure, the first storage control apparatus and thesecond storage control apparatus are connected in series when seen fromthe host computer and, in this situation, the second storage controlapparatus can be operated as an apparatus for extending the functionsof, for example, the first storage control apparatus. This will bedescribed more specifically. The first storage control apparatusreceives from the host computer also a data input/output requestdirected to the second storage control apparatus as the first datainput/output request in addition to a data input/output request directedto itself through the first communication path (corresponding to a firstnetwork described later) constituted of, for example, SAN. At thisstage, if the received data input/output request is directed to thesecond storage control apparatus, the first storage control apparatustransmits the data input/output request to the second storage controlapparatus through a second communication path (corresponding to a secondnetwork described later). That is, the first storage control apparatusfunctions as a relay apparatus between the host computer and the secondstorage control apparatus.

The second data input/output request relayed by the first storagecontrol apparatus to the second storage control apparatus can bearranged such that it is transmitted in a format or protocol as in thefirst data input/output request received by the first storage controlapparatus from the host computer, or such that it is transmitted in aformat or protocol that has been changed in the first storage controlapparatus into that of the second storage control apparatus. When it isarranged that communications between the first storage control apparatusand the second storage control apparatus are carried out using SCSIcommand conforming to ANSI (American National Standards Institute) or astandardized or normalized format or protocol, no special specificationis required as a part of the structure of the second storage controlapparatus as far as the second storage control apparatus has a standardcommunication interface. Therefore, in a storage center such as, forexample, an IDC (Internet Data Center), even when a change in operationhas been carried out in which the first storage control apparatus hasbeen introduced as a new-model disk array apparatus and the old diskarray apparatus that has been used is used being connected in series tothe first storage control apparatus, no special specification change ormodification is required for the second storage control apparatus. Whenthe second storage control apparatus is an optional block device (anapparatus for random accesses represented by a disk apparatus), theinvention can be applied. That is, when the second storage controlapparatus is a large-scale storage control apparatus having high-levelcontrol functions equivalent to those of the first storage controlapparatus, i.e., an optical disk apparatus with a block accessinterface, the invention can be applied.

It can be arranged that the first storage control apparatus storesinformation concerning a storage device for which the second storagecontrol apparatus executes data input/output processes and the firststorage control apparatus determines based on the stored informationconcerning the storage device whether it will transmit to the secondstorage control apparatus the second data input/output requestcorresponding to the first data input/output request.

As the example of the information concerning the storage device, thereis information described in structure information management tabledescribed later. As practical examples, there is management informationof storage area of one or more logic volume(s) organized on a storagearea provided by a storage device, information concerning theperformance of the logic volume, information concerning storagecapacities and information concerning remaining amounts.

For example, when the first data input/output request is a data write-inrequest, the determination of whether to transmit the second datainput/output request to the second storage control apparatus or not iscarried out based on whether the data size of the data to be written inthe logic volume of the second storage control apparatus in response tothe data write-in request is within the range of the storage capacity ofthe logic volume. Furthermore, for example, when it has been determinedthat the data input/output request cannot be normally processed in thesecond storage control apparatus because, for example, the size of thedata to be written in exceeds the capacity of the logic volume, thefirst storage control apparatus does not relay the second datainput/output request to the second storage control apparatus.

In this manner, since it is arranged that the first storage controlapparatus executes the process that should be originally executed by thesecond storage control apparatus, taking the role of the second storagecontrol apparatus, even in a structure in which the second storagecontrol apparatus is connected in series to the first storage controlapparatus as described above, no special mechanism is required to beprovided to the second storage control apparatus. According to the abovefunction, the logic volume in the second storage control apparatus isprovided to the host computer as if the logic volume were a logic volumeof the first storage control apparatus.

It can be arranged that the first storage control apparatus storesaccess limit information concerning a storage device for which thesecond storage control apparatus executes data input/output processes,and the first storage control apparatus, when it has received the firstdata input/output request, determines by referring the contents of thereceived request to the access limit information whether to transmit tothe second storage control apparatus the second data input/outputrequest corresponding to the first data input/output request or not.There can be cases where the access limit information stored by thefirst storage control apparatus is, for example, registered from amanagement computer connected to the first storage control apparatus, orcreated and stored by the first storage control apparatus based on thereceived access limit information or the information as the basis of theaccess limit information that has been transmitted from the secondstorage control apparatus to the first storage control apparatus.

More specifically, for example, it is arranged that, when the secondstorage control apparatus organizes one or more logic volume(s) on astorage area provided by the storage device for which the second storagecontrol apparatus itself executes data input/output processes, the firststorage control apparatus stores the correlation X between IDs given toeach host computer and an ID of the logic volume to which the hostcomputer can make access and the first storage control apparatusdetermines whether to transmit the second data input/output request tothe second storage control apparatus by referring the correlationbetween the ID of the host computer that is the source of the requestdescribed in the first data input/output request and the logic volume towhich a data input/output process of the request described in the firstdata input/output request is directed, to the correlation X.

For example, in a storage system operated in an IDC, a storage controlapparatus such as a disk array apparatus is not so rarely operated suchthat it carries out services to a plurality of host computers. In thiscase, each host computer often limits the storage control apparatusesthat can access to that host computer. The access limit is generallycarried out by, for example, managing the combinations such as portnumbers or switch numbers of WWN or Fiber Channel switches such aszoning or LU masking when a host computer and storage controlapparatuses are connected by SAN. In short, in this method, it isarranged that the first storage control apparatus executes the processesconcerning the access limit taking the role of the second storagecontrol apparatus when such access limit is required to be carried outbetween the host computer and a logic volume of the second storagecontrol apparatus.

It can be arranged that a plurality of routes are included in the secondcommunication path, the first storage control apparatus receivesinformation concerning the second communication path from a relayapparatus existing on the second communication path and the firststorage control apparatus determines, based on the information, a routefor transmitting the second data input/output request. The informationconcerning the second communication path is, for example, networktopology information, information of nodes in the network etc.conforming to the Fiber Channel standard, the SCSI standard or the iSCSIstandard. The relay apparatus is, for example, a Fiber Channel switch, aFiber Channel director, a Fiber Channel hub, an iSCSI router, an iSCSIswitch etc.

The determination of the route is carried out based on at least any oneof the conditions such as performance, reliability and stability of theplurality of paths grasped based on the information concerning thesecond communication path.

It can also be arranged that each of the first and the second storagecontrol apparatuses respectively organizes one or more logic volume(s)on a storage area provided by the storage device for which the first andthe second storage control apparatuses execute respective datainput/output processes, the second storage control apparatus has asecond logic volume being the target of data input/output processes ofthe second storage control apparatus and storing data of the first logicvolume being the target of data input/output processes of the firststorage control apparatus, the first storage control apparatus receivesa data input/output request from the host computer and updates thecontents of the first logic volume in response to the received request,the first storage control apparatus transmits to the second storagecontrol apparatus a data input/output request instructing to the secondlogic volume an execution of a data update process corresponding to theupdating, the second storage control apparatus receives the datainput/output request and updates the contents of the second logic volumein response to the received request, and the first storage controlapparatus stores information for grasping data not yet reflected on alogic volume of the second logic volumes among the data in the firstlogic volume. The information for grasping data not yet reflected is,for example, information describing whether the data in the first logicvolume is reflected on the second logic volume in units of areaorganized in zones on a storage area in the first logic volume.

The information grasped in this manner is used, for example, in a casewhere updating to the second logic volume has been impossible due to anetwork failure etc., however, the failure has been recovered thereafterand data not yet reflected on the second logic volume is reflected. Morespecifically, for example, first, the first storage control apparatustransmits to the second storage control apparatus a data write-inrequest directed to the second logic volume concerning the data not yetreflected on the second volume, that has been grasped from theinformation for grasping the data not yet reflected, and the secondstorage control apparatus receives the data input/output request andexecutes to the second logic volume a write-in process corresponding tothe data write-in request. In this manner, by arranging that the firststorage control apparatus grasps the data not yet reflected on thesecond logic volume, it is not necessary to provide a special mechanismto the second storage control apparatus.

It can be arranged that each of the first and the second storage controlapparatuses organizes one or more logic volume(s) on a storage areaprovided by a storage device for which the first and the second storagecontrol apparatuses execute respective data input/output processes, thefirst storage control apparatus, when it writes new data in a firstlogic volume for which the first storage control apparatus executes datainput/output processes, has transmitted to the second storage controlapparatus a data write-in request of the old data stored in the area forwrite-in of the new data before the write-in process is executed, thesecond storage control apparatus receives the data write-in request andwrites the old data in the second logic volume being the target of datainput/output processes of the second storage control apparatus, thesecond storage control apparatus transmits to the first storage controlapparatus the storage position of the old data in the second logicvolume, and the first storage control apparatus stores the storageposition of the new data in the first logic volume and the storageposition of the old data in the second logic volume transmitted asabove, relating both of them to each other.

A specific example for this method is, for example, a snapshot functiondescribed later. This function enables the data stored at a past time inthe logic volume of the first storage control apparatus to be referredto. In this method, the data at a past time, i.e., the old data isstored in the logic volume of the second storage control apparatus.

Furthermore, the first storage control apparatus stores informationdesignating the storage position of the old data in the logic volume ofthe second storage control apparatus by relating the information to thestorage position where the old data was stored in the logic volume ofthe first storage control apparatus. By utilizing this, the firststorage control apparatus can provide to the host computer the old datacorresponding to the read-out request when, for example, a read-outrequest for an old data stored in a certain storage position in thefirst logic volume has been issued from the host computer.

It can be arranged that, when the first storage control apparatus hasreceived from the host computer a data write-in request of new data forwriting the new data to the first logic volume being the target of datainput/output processes of the first storage control apparatus, the firststorage control apparatus transmits to the second storage controlapparatus the data write-in request of the new data without writing thenew data to the first logic volume, the second storage control apparatusreceives the data input/output request and writes the new data to asecond logic volume being the target of data input/output processes ofthe second storage control apparatus, the second storage controlapparatus transmits to the first storage control apparatus the storageposition of the new data in the second logic volume, the first storagecontrol apparatus stores the storage position of the old data in thefirst logic volume and the storage position in the second logic volumeof the new data to be transmitted, relating both of them to each other.This method also relates to the snapshot function. However, in thismethod, being different from the former snapshot function, it isarranged that the old data is stored in the first storage controlapparatus and the newest data in the logic volume of the first storagecontrol apparatus is stored on the second storage control apparatusside.

As described above, according to the invention, the second storagecontrol apparatus can be effectively utilized when the system isoperated such that it has a copy of data, and when services such as thesnapshot are provided. Especially when a first storage control apparatusis introduced as a substituting apparatus for the second storage controlapparatus, the old-type second storage control apparatus can beeffectively utilized continuously after introducing the first storagecontrol apparatus. Therefore, effects such as reduction of the operationload of the storage system and reduction of the operation costs can beobtained.

<Overview of the System>

FIG. 1 shows the structure of a storage system described as oneembodiment of the invention. This storage system is operated in, forexample, an IDC. In the figure, a first storage control apparatus 10 andthe second storage control apparatus 20 are disk array apparatuses thatoperate storage devices such as, for example, disk drives, in RAID(Redundant Array of Inexpensive Disks) scheme, execute data input/outputprocesses to the storage devices using a data input/output control unit19 in response to data input/output requests such as data write-inrequests and data read-out requests transmitted from a host computer 30,and function as data storage for the host computer 30. The first and thesecond storage control apparatuses 10, 20 may be sometimes also referredto as the “transfer storage control apparatus” and the “ordinary storagecontrol apparatus,” respectively in the specification. It is simply tomore clearly distinguish the first and the second storage controlapparatuses without intended to give any specific interpretation.

The host computer 30 is connected to the first storage control apparatus10 through a first network 50 and the second storage control apparatus20 is connected to the first storage control apparatus 10 through asecond network 51. The first and the second networks are, for example,SANs (Storage Area Network) consisting of network devices conforming tothe Fiber Channel. However, the networks are not limited to this but canbe LANs (Local Area Network), general telephone lines, dedicated linesand networks of main frame system such as a protocol conforming to ESCON(Enterprise Systems CONnection) or FICON (Fiber CONnection).

The first storage control apparatus 10 receives a data input/outputrequest transmitted from the host computer 30 through the first network50. The second storage control apparatus 20 receives the datainput/output request from the first storage control apparatus 10 throughthe second network 51. The second storage control apparatus 20 can beanapparatus having an equivalent performance as or a higher performancethan that of the first storage control apparatus 10, or can be anapparatus having a performance lower than that of the first storagecontrol apparatus 10.

As a case where the operation form shown in FIG. 1 is employed, thereis, for example, a case where the operation of a storage system has beenchanged such that the first storage control apparatus 10 is newlyintroduced as a succeeding apparatus of the second storage controlapparatus 20 to a storage system operated in a form in which the secondstorage control apparatus 20 is connected to the host computer 30, andthe second storage control apparatus 20 functions as an apparatus forextending or supporting the functions of the first storage controlapparatus 10.

The basic apparatus structure of the first storage control apparatus 10will be described. The first storage control apparatus 10 is mountedwith a storage apparatus 60 with one or more disk drive(s), as a storagedevice for providing a data storage area. The storage apparatus 60 canbe structured such that it is connected to outside of the housingthrough, for example, a communication line conforming to the SCSIstandard. As described above, the disk drive(s) are operated in RAIDscheme, for example.

The first storage control apparatus 10 organizes one or more logicvolume(s) 11 (hereinafter referred to as “logic volume”) on a storagearea provided by one or more disk drive(s). Each logic volume 11 isrespectively given a specific identifier (hereinafter referred to as“LUN (logical unit number)”). A LUN for designating a data storage areais described in a data input/output request transmitted by the hostcomputer 30 to the first storage control apparatus 10. The first storagecontrol apparatus 10 has a function for providing a storage area to thehost computer 30 by a LUN designation.

A microprocessor 12 (hereinafter referred to as “MP”) executes thevarious processes of the first storage control apparatus 10 such as, forexample, data input/output processes to the disk drive(s). MP 12consists of one or more CPU(s). A microprocessor specialized in certainfunctions can be provided as MP 12. A cache memory 13 is mainly used forstoring temporarily data input to/output from the disk drive(s) such aswrite-in data to the disk drive(s) and read-out data from the diskdrive(s).

A control memory 14 is, for example, utilized as a working area for MP12 or is used for storing various control data and tables. For example,a structure information management table 41 described later, a bit map42, an access limit information table 43, an update management table 44etc. are usually stored in this control memory 14.

An external interface 15 is a Fiber Channel interface. The externalinterface 15 connects the first storage control apparatus 10 to thefirst network 50 or the second network 51. The external interface 15 isprovided with a plurality of ports 16 connected to ports of a FiberChannel switch constituting a SAN. As is known in the field of the FiberChannel, a WWN (world wide name) being an identifier for identifying anapparatus on a SAN is given to each port 16 of the external interface15. The storage apparatus 60 is connected to the first storage controlapparatus 10 through a device port 19 of a device interface 18.

The first storage control apparatus 10 has been described as above andthe second storage control apparatus 20 also has a same structure as thefirst storage control apparatus 10 concerning the basic structure exceptthe performance and the size of each component contained.

On the other hand, the host computer 30 is, for example, a personalcomputer, a work station or a general-purpose computer and is providedwith a HBA (Host Bus Adapter) (not shown) being a Fiber Channelinterface that is an interface for connecting to the first network 50. AWWN is also given to an HBA.

<Structure Information Management Table>

The second storage control apparatus 20 provides to the first storagecontrol apparatus 10 its own logic volume as a logic volume of the firststorage control apparatus 10. To realize this function, the firststorage control apparatus 10 stores the structure information managementtable 41 shown in FIG. 2.

In this structure information management table 41, informationconcerning a logic volume handled by the first storage control apparatus10 is described. In the structure information management table 41,information concerning not only the logic volume for which the firststorage control apparatus 10 executes data input/output processes(hereinafter referred to as “first logic volume”) but also the logicvolume for which the second storage control apparatus 20 executes datainput/output processes (hereinafter referred to as “second logicvolume”) is described (In FIG. 2, only the information concerning thesecond logic volume 21 is shown).

In FIG. 2, the port IDs of external interfaces connected to the logicvolumes are described in a column 210 for port ID. The WWNscorresponding to the port IDs are described in a column 211 for WWN. TheLUNs for each logic volume are described in a column 212 for LUN. Thecapacities of storage areas provided by the first and the second logicvolume 11 and 21 are described in a column 213 for capacity.

Identifiers of the second logic volume related to their ports and LUNsare described in a column 214 for mapping LUN. That is, when adescription exists in the column for mapping LUN, that means the logicvolume is the second logic volume 21, therefore, other logic volumes arethe first logic volumes 11.

The contents of the structure information management table 41 is, forexample, registered by an operator from a management computer (notshown) etc. connected to the first storage control apparatus 10 and thefirst storage control apparatus 10 has an information collectionfunction (discovery function) described later. With this function, thefirst storage control apparatus 10 detects an apparatus connected to thesecond network 51 through the second network 51, transmits to thedetected apparatus a transmission request of the information concerningthe logic volumes of the detected apparatus, receives informationtransmitted as per the request and registers the information in thestructure information management table 41.

The apparatus being the destination of the information for the apparatusexists on the second network 51 can be otherwise predetermined fixedly.Various settings for the conditions are possible such that only theproducts from a certain manufacturer are targeted by checking the modelnumber of the apparatuses, that only the logic volumes having capacitiesmore than a certain capacity are targeted and that only the logicvolumes connected to a predetermined port are targeted.

The first storage control apparatus 10 provides to the host computer 30the second logic volume 21 of the second storage control apparatus 20 asif it were the first logic volume 11 of the first storage controlapparatus 10, using the structure information management table 41described above and in a mechanism described later. That is, the hostcomputer 30 can execute to the first storage control apparatus 10 a datainput/output request directed to the logic volume 21 of the secondstorage control apparatus 20.

Since the first storage control apparatus 10 stores the structureinformation management table 41 as described above, the first storagecontrol apparatus 10 can transmit a response by a proper responsemessage to the host computer 30 not only when a data input/outputrequest has been transmitted from the host computer 30 but also evenwhen, for example, commands such as “Inquiry” or “Read Capacity” hasbeen transmitted from the host computer 30 directed to the second logicvolume 21.

<Data Input/Output Process>

Next, the operation of the storage system in a case where a datainput/output request is issued from the host computer 30 to the firststorage control apparatus 10 through the first network 50 directed tothe first logic volume 11 or the second logic volume 21 will bedescribed.

FIG. 3 shows an example of the data format of a data input/outputrequest transmitted from the host computer 30 to the first storagecontrol apparatus 10. In this figure, the column 310 for host ID showsan identifier of the host computer 30 having transmitted the datainput/output request and, for example, the WWN of the HBA of the hostcomputer 30 is described in it. The column 311 for port ID shows theport ID of a port connected to the logic volumes 11 and 21 that are thetargets of process of the data input/output request. The column 312 forLUN shows the ID of a logic volume being the target of the process ofthe data input/output request. A column 313 for address and a column 314for data length are set when, for example, the data input/output requestis a data read-out request and, in this case, the head addresscontaining the data of read-out source of the logic volumes 11 and 21being the read-out sources is set in the column 313 for address and thedata length of the data being the target of the read-out process is setin the column 314 for data length.

A process of the storage system for the case where the data input/outputrequest transmitted from the host computer 30 is a data write-in requestwill be described with FIG. 4. First, the first storage controlapparatus 10 receives a data write-in request from the host computer 30through the first network 50 (S412) and stores in the cache memory 13write-in target data received with the data write-in request (S413).

Next, the first storage control apparatus 10 refers to the structureinformation management table 41 to judge whether the data write-inrequest can be executed or not. The case where it can not be executedis, for example, that the logic volume being the target of the processof data input/output request does not exist or that, even when the logicvolume exists, the size of the data being the target of the write-inprocess exceeds the size of the storage area of the logic volume.

The first storage control apparatus 10 checks referring to the structureinformation management table 41 whether the logic volume being thetarget of the process really exists, or whether the logic volume beingthe write-in destination has an enough capacity for being written thedata to be written in by the data write-in request and judges whether adata input/output request corresponding to the data input/output requestcan be executed (S414). At this stage, if the first storage controlapparatus 10 judges the data input/output request cannot be executed asa result of this judgment, it transmits to the host computer 30 amessage in which that judgment is described and completes the processcorresponding to the data input/output request (S415 in FIG. 4).

Furthermore, the first storage control apparatus 10 stores in thecontrol memory 14 the access limit information table 43 in which thecombinations of the port ID or WWN of the host computer 30 of therequest source of the data input/output request, the first logic volume11 or the second logic volume 21 to be the request target of the datainput/output request and access type (read-out/write-in) are registered.There are cases where the contents of this access limit informationtable 43 is registered by an operator from a management computer (notshown) etc. connected to the first storage control apparatus 10, wherethe first storage control apparatus 10 receives the access limitinformation or information being the basis of that information,transmitted from the second storage control apparatus 20 and the firststorage control apparatus 10 creates and stores the contents based onthat information. The latter operation can be carried out, for example,when the second storage control apparatus 20 itself has a mechanismconcerning an access limit function for the logic volume 21 of thesecond storage control apparatus 20.

The first storage control apparatus 10 executes an access limit processthat is a process for checking whether the combination of the ID of theport having received the data input/output request or WWN of the hostcomputer 30 being the source described in the data input/output request,and the port ID of the first logic volume 11 or the second logic volume21 designated in the data input/output request as the write-indestination matches the authorized access conditions (S416).

The concept of an access limit process is shown in FIG. 5A. The firststorage control apparatus 10 checks whether the data input/outputrequest from the host computer 30 matches the access limit in the accesslimit information table 43 and, if they do not match to each other, doesnot execute any process corresponding to the data input/output request,transmits a message in which the result is described and completes theprocess corresponding to the data input/output request (S415).

The above processes concerning the access limit are executed not onlywhen the logic volume being the target of the process of the datainput/output request is the first logic volume 11 but also when thelogic volume being the target is the second logic volume 21. That is,the first storage control apparatus 10 substitutes in carrying out aresearch of the access limit to the second logic volume 21.

On the other hand, as shown in FIG. 5B, when seen from the hostcomputer, there is no distinction whether the logic volume being thetarget of a data input/output request belongs to the first storagecontrol apparatus 10 or to the second storage control apparatus 20. Thehost computer 30 simply grasps whether a logic volume existing on thenetwork is accessible or not accessible.

As a result of the above processes, when the logic volume being thetarget of the process of the data input/output request has been judgedto be possible to be written in (that is, the logic volume exists, itscapacity is large enough and its access limit has no problem), the firststorage control apparatus 10 transmits a data write-in request to thesecond storage control apparatus 20 (S417). The second storage controlapparatus 20 receives this data write-in request and writes the write-indata in the second logic volume 21.

The data write-in request in this case conforms to the same protocol(for example, the data format is same) as that of the data write-inrequest directly received from the host computer 30 by the secondstorage control apparatus 20. Therefore, when the operation of thesecond storage control apparatus 20 is changed, because the firststorage control apparatus 10 is newly introduced, such that the secondstorage control apparatus 20 functions as an apparatus for providinglogic volumes to the first storage control apparatus 10, there is noneed to carry out any change or modification especially for theapparatus structure and specification of the second storage controlapparatus 20. Therefore, an effective use of the second storage controlapparatus 20 becomes possible with the minimal effort and at a low cost.

The access limit function of the first storage control apparatus 10described above can be applied in various environments such as the casewhere the second storage control apparatus 20 does not have any accesslimit function and the first storage control apparatus 10 dedicatedlysupport the access limit function of the second storage controlapparatus 20 in addition to the case where the second storage controlapparatus 20 originally has a function concerning the access limit.

The first storage control apparatus 10, when having transmitted a datainput/output request to the second storage control apparatus 20,transmits to the host computer 30 a message to communicate thecompletion of the write-in process without waiting for the completionnotice of the process of the data input/output request from the secondstorage control apparatus 20 (S415). Therefore, the host computer 30 canconfirm quickly the response to the data input/output request and canstart the following process quickly without a long waiting time.

A write-in process has been described as above. However, in the case ofa read-out process from a logic volume, the process is also executed ina same mechanism except that data is transferred in the oppositedirection in contrast to the above case for a write-in process. For datainput/output requests except the ones for write-in and read-outprocesses, the first storage control apparatus 10 returns responses asusual to the host computer 30.

As described above, in the storage system, the host computer 30 accessesthe second logic volume as if it were a logic volume in the firststorage control apparatus 10. Furthermore, even when the logic volumebeing the target of a data input/output request is originally for thesecond storage control apparatus 20, the management load and themanagement cost for security can be minimized since the judgment ofwhether a data input/output request can be normally processed andmanagement of access right setting etc. can be carried out concentratedand intensively in the first storage control apparatus 10. Furthermore,by executing the processes to be executed by the second storage controlapparatus 20 using the first storage control apparatus 10, the processload on the second storage control apparatus 20 side can be reduced.

<Data Copy Function>

Next, a data copy function executed in this storage system will bedescribed. The function described in this section is utilized forrealizing functions such as, for example, data replication or datamirroring and is a function that works such that the second storagecontrol apparatus 20 also has a logic volume having the same contents asthat of a logic volume of the first storage control apparatus 10.

The first logic volume 11 being the copy source and the second logicvolume 21 being the copy destination can be provided in a relation of1:N in addition to in a relation of 1:1. The case where they areprovided in the relation of 1:1 will be described as an example forsimplification of description. However, even in the case where they areprovided in the relation of 1:N, the basic process can be executedsimilarly simply because a plurality of relations of 1:1 exist.

In order to realize the data copy function, for example, a mechanism formanaging the difference of the contents between the first logic volume11 and the second logic volume 21 is necessary as a preparation for thecase where a communication failure occurs on the second network 51. Asthis mechanism, the one in which a bit map where a bit is related toeach block or block group organized in zones in the storage area of alogic volume of the first storage control apparatus 10 is prepared andevery bit for which a difference is generated between those logicvolumes is made “on” is known.

FIG. 6 illustrates processes of the storage system concerning the datacopy function. When the first storage control apparatus 10 has receivedfrom the host computer 30 a data write-in request to the logic volumebeing the copy source (S611), it stores the received request in its owncache memory 13 (S612). The first storage control apparatus 10 transmitsa write-in process completion report to the host computer 30 at themoment when the write-in data has been stored in the cache memory 13(613).

When the first storage control apparatus 10 has transmitted the write-inprocess completion report to the host computer 30, it makes on the bitscorresponding to the update address of the logic volume being thewrite-in destination of this write-in process in the bit map 42 (S614).

Next, the first storage control apparatus 10 starts the process formatching the contents of the logic volumes 11 and 21 being the copysource and the copy destination with each other at a proper timing suchas the time when an instruction has been issued from a managementcomputer (not shown).

First, the first storage control apparatus 10 refers to the bit map 42and transmits to the second storage control apparatus 20 a write-inrequest of the data stored in a storage area of the logic volume 11 ofthe copy source corresponding to blocks or block groups that havediscord in contents, i.e., that the bit is on (S615).

When the second storage control apparatus 20 has received the datawrite-in request and the write-in data, it writes the received write-indata to the targeted storage area of the second logic volume 21 beingthe copy destination and transmits to the first storage controlapparatus 10 a write-in completion report (S616).

At the moment when the first storage control apparatus 10 receives thedata write-in completion report from the second storage controlapparatus 20, the first storage control apparatus 10 sets off the bit ofthe bit map 42 corresponding to the storage area of the data written inthe copy destination (S617). That is, the contents of the bit map 42 ismanaged at real time such that only the bits corresponding to thestorage area where the contents of the first logic volume 11 and thesecond logic volume 21 are different. In this manner, the contents ofthe logic volumes being the copy source and the copy destination aresynchronized with each other.

It is not necessary that the storage capacities of the logic volumesbeing the copy source and the copy destination are always same. In thecase where the logic volumes being the copy source and the copydestination are different as described above, for example, addresses areconverted and stored in another volume, or the data size is reducedusing a compression process and is stored.

In the above description, the first logic volume 11 is the copy sourceand the second logic volume 21 is the copy destination. However, incontrast to this, it may be structured that the copy source is thesecond logic volume 21 and the copy destination is the first logicvolume 11.

<Re-Synchronization Process>

Next, a re-synchronization process executed for the case where thecontents of the first logic volume 11 and the second logic volume 21 aredifferent due to a failure of the second storage control apparatus 20 orthe second network 51, etc. And, thereafter, the failure is recoveredand it is possible to synchronize the contents of the logic volumes 11and 21.

The first storage control apparatus 10 detects a failure of the secondnetwork 51 by, for example, a time-out of communication between thefirst and the second storage control apparatuses 10 and 20. Thedifference of the contents can be caused not only by the failure of thesecond network 51 but also by operations of a user such as back-upprocess and application tests.

First, the processes for the case where the first storage controlapparatus 10 detects a failure of the second network 51 will bedescribed. When the first storage control apparatus 10 has detected afailure, it switches the operation from the normal operation conditiondescribed above to a separated condition (S621) and stops a transmissionprocess to the second storage control apparatus 20 of a data write-inrequest about update finite difference data. As to a write-in process tothe first logic volume 11, the processes from (S611) to (S614) areexecuted (S622). Therefore, the bits on the bit map corresponding to theblocks or block groups updated during the separated condition are set toon and the difference between the first logic volume 11 and the secondlogic volume 21 is managed.

Next, when the failure has been recovered and the second logic volume 21becomes available, first, the first storage control apparatus 10transmits to the second storage control apparatus 20 a data write-inrequest directed to the second logic volume 21 about the data stored ina storage area of the first logic volume 11 corresponding to the blocksor block groups of which the bit in the bit map 42 is on.

When the second storage control apparatus 20 has received the datawrite-in request, it writes the write-in data received with the requestto a storage area corresponding to a targeted logic volume. In thiswrite-in process, for example, when the system is operated such that thedata stored in a storage area of a certain address in the logic volume11 being the copy source is stored in a storage area designated by thesame address in the logic volume 21 being the copy destination, the datais stored in a storage area of the second logic volume 21 designated bythe same address as the address in the first logic volume 11 where thedata has been stored (S623).

In the above processes, it is arranged that the first storage controlapparatus 10 transmits to the second storage control apparatus 20 onlythe data stored in the updated storage area. Therefore, the amount ofthe data transmitted to the second network 51 can be almost minimized.When the re-synchronization process of the contents of those logicvolumes has been completed in this manner, the first storage controlapparatus 10 re-starts the transmission of the data write-in request ofthe updated finite difference data.

The above processes are on the premise that the update of the logicvolume 21 being the copy destination is not executed as far as the logicvolume 11 being the copy source has not been updated. However, an updateof the logic volume 11 being the copy destination may have been executedbefore an update of the logic volume 21 being the copy source isexecuted depending on a form of use of the storage system. In this case,the contents of those logic volumes cannot be re-synchronized using thebit map 42 and the re-synchronization process is executed, for example,in a manner in which all the data in the logic volume 11 of the firststorage control apparatus 10 is transferred to the logic volume 21 ofthe second storage control apparatus 20.

It can be arranged that the update situation of the second logic volume21 is managed by managing a bit map concerning the second logic volume21. In this case, the bit map is stored, for example, in the controlmemory 14 of the first storage control apparatus 10, in a control memory(not shown) of the second storage control apparatus 20 or in the logicvolume 21. Furthermore, in this case, re-synchronization can be executedby, for example, transferring the data stored in blocks or block groupsthat have been updated from the first logic volume 11 and writing it tothe second logic volume 21.

<Snapshot>

(1) Snapshot Function 1

Next, snapshot function will be described. This function enables thedata stored in a logic volume at a past time designated by a user to beobtained. Whether the snapshot function is operated or not can be setfor each logic volume.

The case where the first storage control apparatus 10 operates thesnapshot function for the first logic volume 11 will be described. Thesnapshot function described here is a function that stores in the secondlogic volume 21 old data stored in a storage area of the first logicvolume 10 being the target of a write-in process and enables old data tobe utilized afterward, for example, from the host computer 30 when awrite-in process has been executed to the first logic volume with newdata.

FIG. 7 illustrates the snapshot function in the storage system. In thisprocess, a logic volume 21 for storing the old data for the snapshotfunction has been secured in the second storage control apparatus 20. Inthis case, the structure can be arranged that one logic volume 21 isshared for the snapshot for a plurality of the first logic volume 11 ofthe first storage control apparatus 10.

The first storage control apparatus 10 stores in the control memory 14the update management table 44 in which the correlation is registeredbetween addresses designating the storage area where writing has beeneffected among the storage areas of the first logic volume 11 andaddresses of the second logic volume 21 which is a refuge for the olddata stored in that storage area.

The mechanism for realizing the snapshot function will be described.First, when the first storage control apparatus 10 has received a datawrite-in request directed to the first logic volume 11 transmitted fromthe host computer 30 (S711), the first storage control apparatus 10stores in the cache memory 13 the write-in data (new data) received withthe data write-in request (S712).

Next, the first storage control apparatus 10 reads out the data alreadystored in the storage area of the first logic volume 11 being thedestination of the data write-in process (old data) being the target ofthis data write-in process and stores the old data in the cache memory13 (S713). Thereafter, the first storage control apparatus 10 writes thewrite-in data received from the host computer 30 (new data) in thestorage area (S714).

The first storage control apparatus 10 transmits a write-in completionreport to the host computer 30 at the moment when it has stored thewrite-in data in the cache memory 13. Therefore, the real write-inprocess of the write-in data in the first logic volume 11 may beexecuted after the write-in completion report has been transmitted.

Next, the first storage control apparatus 10 transmits the old datastored in the cache memory 13 to the second storage control apparatus20. When the second storage control apparatus 20 has received the olddata, the second storage control apparatus 20 stores the data in thesecond logic volume 21. At this stage, the second storage controlapparatus 20 transmits the storage position of the second logic volume21 where the old data is stored with an address indicating the originalstorage position in the logic volume 11 of the first storage controlapparatus 10 where the old data has been stored (this address isreceived from the first storage control apparatus 10 with, for example,the write-in data). On the other hand, the first storage controlapparatus 10 receives the transmitted storage position and stores it inthe update management table 44 of the control memory 14 (S715). Asdescribed above, the old data (hereinafter referred to as “snapshot”) isstored in the second logic volume 21 of the second storage controlapparatus 20.

When, for example, the first storage control apparatus 10 has receivedfrom the host computer 30 a data read-out request for the first logicvolume 11 being the target of creating a snapshot, the first storagecontrol apparatus 10 executes a read-out process by an ordinary processfrom the first logic volume 11 of the first storage control apparatus 10and transmits the read out data to the host computer 30.

On one hand, when, for example, the first storage control apparatus 10has received from the host computer 30 a data read-out request for theold data of the logic volume 11 and an area corresponding to the storagearea designated by the read-out request is stored in the updatemanagement table 44, the first storage control apparatus 10 transmits tothe second storage control apparatus 20 a read-out request of thetargeted data from the second logic volume 21. The second storagecontrol apparatus 20, in response to this, transmits the targeted olddata to the first storage control apparatus 10. Then, the first storagecontrol apparatus 10 receives the transmitted old data and transmits itto the host computer 30.

On the other hand, when the storage area designated by the read-outrequest is not stored in the update management table 44, the firststorage control apparatus 10 reads out the targeted data from the firstlogic volume 11 of the first storage control apparatus 10 and transmitsit to the host computer 30.

(2) Snapshot Function 2

Next, another method for realizing the snapshot function will bedescribed referring to FIG. 8.

In this method, when a data write-in request for the first logic volume11 of the first storage control apparatus 10 has been transmitted fromthe host computer 30, the first storage control apparatus 10 writeswrite-in data (new data) to the second logic volume 21 of the secondstorage control apparatus 20 without executing any update of the firstlogic volume 11 itself. That is, different from the above-describedmethod, in an ordinary write-in process, new data to be originallywritten in the first logic volume 11 is not written to the first logicvolume 11 and the old data is kept stored as it is in the first logicvolume 11 and the new data is stored in the second logic volume 21.

In this method, a data write-in request for the first logic volume 11 ofthe first storage control apparatus 10 has been transmitted from thehost computer 30 and, when the first storage control apparatus 10 hasreceived the data write-in request (S811), it stores in the cache memory13 the write-in data (new data) transmitted with the data write-inrequest (S812).

Next, the first storage control apparatus 10 transmits to the secondstorage control apparatus 20 the new data stored in the cache memory 13and a data write-in request for the new data. Then, the second storagecontrol apparatus 20 having received this stores the new data in thesecond logic volume 21.

For the above case, as the addresses designating the storage area in thesecond logic volume 21 of the new data, there is, for example, anaddress where no new data has been stored yet is designated. Thisaddress is transmitted from the second storage control apparatus 20 tothe first storage control apparatus 10 and the first storage controlapparatus 10 stores the address in the update management table 44relating it to an address designated as a write-in destination of thedata write-in request. (S813). This relating is carried out by, forexample, exchanging between the first storage control apparatus 10 andthe second storage control apparatus 20 the information necessary forthe relating.

In a case where a snapshot is created as described above, when a dataread-out request is issued from the host computer 30, the first storagecontrol apparatus 10 first checks the update management table 44. Then,if the address of the read-out destination designated by the read-outrequest is not contained in the update management table 44, the firststorage control apparatus 10 reads out the targeted data from the firstlogic volume 11 and transmits the data to the host computer 30.

On the other hand, if the address of the read-out destination iscontained in the update management table 44, the first storage controlapparatus 10 transmits to the second storage control apparatus 20 aread-our request for the data at the address of the second logic volumeof the second storage control apparatus 20 stored in the updatemanagement table 44 being related to the address.

When the second storage control apparatus 20 has received the read-outrequest, the second storage control apparatus 20 reads out the data fromthe second logic volume 21 and transmits the data to the first storagecontrol apparatus 10. When the first storage control apparatus 10 hasreceived the data, it transmits the data to the host computer 30 (S814).

When, for example, the first storage control apparatus 10 has receivedfrom the host computer 30 a data read-out request for the old data of acertain first logic volume 11, and the storage area designated by theread-out request is stored in the update management table 44, the firststorage control apparatus 10 reads out the data from the logic volume 11of the first storage control apparatus 10 and transmits the data to thehost computer 30.

In the above description, it is arranged that the update managementtable 44 is stored in the control memory 14 of the first storage controlapparatus 10, however, it can also be arranged that the updatemanagement table 44 is stored in a control memory (not shown) of thesecond storage control apparatus 20, the second logic volume 21 oranother logic volume 21 in the second storage control apparatus 20. Whenit is arranged as described above, the snapshot function can be realizedwithout providing any special mechanism to the second storage controlapparatus 20.

(3) Reflecting of New Data

When the snapshot function 2 described above operates, the new data isnot reflected on the first logic volume 11. However, there are timeswhen old data becomes not necessary to be stored in the first logicvolume 11 and new data stored in the second logic volume 21 is requiredto be reflected on the first logic volume 11 such as when, for example,the old data of the first logic volume 11 has finished its role due tothe completion of user's work. Furthermore there are times when new datais required on the first logic volume 11 at a timing regularly or notregularly since the storage area of the second logic volume 21 isdecreased by new data stored one after another in the second logicvolume 21. Then, a mechanism for reflecting new data on the first logicvolume 11 for these cases will be described.

The description will be given referring to FIG. 9. First, a read-outrequest of new data is transmitted from the first storage controlapparatus 10 to the second storage control apparatus 20 (S911). In thisread-out request, information concerning the storage position of the newdata in the second logic volume 21 is contained.

When the second storage control apparatus 20 has received the read-outrequest, the second storage control apparatus 20 reads out from thesecond logic volume 21 the new data stored in the storage positionidentified from the information and transmits the new data to the firststorage control apparatus 10.

When the first storage control apparatus 10 has received the new data,the first storage control apparatus 10 stores the new data in the cachememory 13 (S912) and writes the new data in the storage position of thefirst logic volume 11 specified by the update management table 44 (i.e.,the storage position in the first logic volume 11, where the new datashould originally be stored, designated in the data write-in requesttransmitted from the host computer 30) (S913).

The new data is reflected on the first logic volume 11 by the abovemechanism. As to new data, it can also be arranged that all the new datastored in the second logic volume 21 are reflected on the first logicvolume 11 simultaneously at a certain timing, or that only the specificnew data selected based on the conditions such as whether the time atwhich the new data was stored in the second logic volume 21 is before apredetermined time is reflected or not.

New data can be reflected on the first logic volume by the abovemechanism for the cases where the old data in the first logic volumefinishes its role due to the completion of user's work, or where storagearea of the second logic volume is required to be released.

In the above mechanism, though the first storage control apparatus 10stores once the new data in the cache memory 13 of the first storagecontrol apparatus 10 itself at the timing when the first storage controlapparatus 10 has received a data write-in request from the host computer30 (for example, (S813) in FIG. 8), the new data is read out from thesecond storage control apparatus 20 and is transmitted to the firststorage control apparatus 10 when the new data is reflected on the firstlogic volume 11. However, this increases the traffic on the secondnetwork 51 in vain.

Then, as shown in FIG. 10, it can be arranged that, for example, whenthe first storage control apparatus 10 has received the data write-inrequest, it keeps the new data temporarily stored in the cache memory 13stored as it is and, when it tries to get the new data reflected on thefirst logic volume 11, as shown in FIG. 11, it writes the new datastored in the cache memory 13 to the first logic volume 11 withoutreading out the new data from the second logic volume 21 (S1111).

In this case, whether the new data is kept stored in the cache memory 13or not is managed by, for example, as shown in the table 1200 in FIG.12, ON or OFF of a flag being related to the cache address designating astorage position of the new data on the cache memory.

In this mechanism, the storage area of the cache memory 13 tends todecrease due to the new data kept stored. Therefore, it can also bearranged that, when the first storage control apparatus 10 has receiveda data write-in request from the host computer 30, whether the new datais kept stored in the cache memory 13 or not is determined depending onthe use status such as the remaining amount of the storage area of thecache memory 13. As shown in the table 1300 in FIG. 13, the remainingamount of the cache memory 13 is grasped by managing the remainingamount of the cache memory 13. When the new data is reflected on thefirst logic volume 11, if, for example, the new data is stored in thecache memory 13, this new data is utilized, and if it is not, the newdata is obtained from the second logic volume 21.

It can be arranged that, when the new data is reflected on the firstlogic volume 11, whether the new data is stored in the cache memory 13is checked and, if it is stored, the read-out request is not transmittedand the new data stored in the cache memory 13 is stored at a storageposition in the first logic volume 11 corresponding to the new data and,if it is not stored, a read-out request for the new data is transmittedto the second storage control apparatus 20 and the new data transmittedback in response to the read-out request is stored in the storageposition of the first logic volume 11 corresponding to the new data.According to this method, a system in which the new data is notnecessarily stored in the cache memory can be flexibly coped with sincethe processes are switched between the cases where the new data isstored in the cache memory and where it is not. It can also be arrangedthat the first storage control apparatus 10 determines whether the newdata is kept stored in the cache memory 13 or not depending on the usestatus of the cache memory 13.

According to the above mechanism, the influence on the second network 51caused by the reflecting of the new data on the first logic volume 11 issuppressed. Furthermore, high-speed processes can be realized since nocommunication is generated between the first and the second storagecontrol apparatus 10 and 20 because the new data can be reflected on thefirst logic volume 11 only with the processes of the first storagecontrol apparatus 10 itself.

<Exchange of Roles of Logic Volumes>

For example, in the above-described data copy function, an exchange ofroles of the copy source and the copy destination between the firstlogic volume 11 and the second logic volume 21 may be desired. Similarlyin the above-described snapshot function, an exchange of roles betweenthe first logic volume 11 and the second logic volume 21 may be desired.

In these cases, it is considered that an exchange of the data stored inthe first logic volume 11 and the data stored in the second logic volume21 is carried out by, for example, transmitting those data respectivelyto the opposite logic volume between the first storage control apparatus10 and the second storage control apparatus 20 through the secondnetwork 51 and their roles are exchanged thereafter. However, in thiscase, the communication on the second network 51 is influenced by theabove transmission.

Then, the first storage control apparatus 10 of this embodiment has amechanism for exchanging those roles at a timing when the contents ofthe first logic volume 11 and the contents of the second logic volume 21becomes same such as, for example, when the contents of the logicvolumes being the copy source and the copy destination are synchronizedin the above-described data copy function, or when the new data isreflected on the logic volume that stored the old data in theabove-described snapshot function.

That is, for example, as shown in the table 1400 in FIG. 14, in the datacopy function, when the first logic volume 11 is set as the copy sourceand the second logic volume 21 is set as the copy destination, it isarranged that the first logic volume 11 is recognized as the copydestination and the second logic volume 21 is recognized as the copysource by the program realizing the data copy function as shown in thetable 1500 in FIG. 15 at a timing when the contents of the logic volume11 and 21 are same and their roles are exchanged with each other.Furthermore, in the snapshot function, for example, as shown in thetable 1600 in FIG. 16, when the first logic volume 11 is used forstoring the old data and the second logic volume 21 is used for storingthe new data, it is arranged that the first logic volume 11 isrecognized as the one for storing the new data and the second logicvolume 21 is recognized as the one for storing the old data by theprogram realizing the snapshot function at a timing when the contents ofthe logic volumes 11 and 21 are same as shown in the table 1700 in FIG.17. The above tables shown in FIG. 14 to FIG. 17 are stored in, forexample, the control memory 14.

According to the above mechanism, the roles of the first logic volume 11and the second logic volume 21 recognized by the program realizing thedata copy function and snapshot function etc. can be exchanged withoutcarrying out any data transmission through the second network 51. In acase where the data copy function and the snapshot function are appliedin a connection structure shown in FIG. 1 as a result of introducing afirst storage control apparatus 10 having a higher performance to anenvironment where a second storage control apparatus 20 is operated,exchanging the roles of the logic volumes 11 and 21 may be desiredafterward for the reason such as that a higher performance should beapplied to the copy source. However, even in this case, according to theabove mechanism, the roles of the logic volumes 11 and 21 recognized bythe program realizing the data copy function and the snapshot functioncan be exchanged without pressuring the second network 51.

<Check Code>

The first storage control apparatus 10 attaches a check code to data tobe stored in the first logic volume 11 for the purpose of securing thedata reliability, etc. The check code is an error correction code (ECC)such as, for example, a check sum, a parity bit, a Hamming code, cyclicredundancy check code (CRC code). The first storage control apparatus 10creates a check code for, for example, at every predetermined length ofdata and attaches it to the data.

The first storage control apparatus 10 has a mechanism for checking theconsistency and the validity of data by, for example, checking whetherany error such as a bit garbling exists in the data or not using thecheck code when the first storage control apparatus 10, for example,reads data from or writes data in the first logic volume 11. The firststorage control apparatus 10 also has a mechanism for correcting errorsand notifying the management computer that it has detected an error. Thefirst storage control apparatus 10 further has a mechanism for carryingout such processes concerning the check code also to the data stored inthe second logic volume 21 of the second storage control apparatus 20.This mechanism will be described referring to FIG. 18.

When a data write-in request received from the host computer (S1811) isto be handled by the second storage control apparatus 20, the firststorage control apparatus 10 creates a check code about a write-in datatransmitted from the host computer 30 attached to the data write-inrequest (S1812) and transmits to the second storage control apparatus 20a data write-in request about the write-in data, to which the createdcheck code is attached (S1813).

The second storage control apparatus 20 receives the data write-inrequest and stores in the second logic volume 21 the write-in data towhich the check code is attached (S1814). At this stage, it can also bearranged that, as shown in FIG. 18, the write-in data and its check codeare stored respectively in different logic volumes of the second storagecontrol apparatus 20, or that each of them are stored respectively inconsecutive storage areas in the same logic volume. It can also bearranged that they are stored respectively in storage areas being notconsecutive in the same logic volume.

In this case, it is arranged that information indicating which data thecheck code is about (for example, an identifier and an address of thelogic volume where the corresponding data is stored) is attached to eachcheck code. When they are stored in different logic volumes, it isarranged that, for example, data input/output requests corresponding toeach of them are transmitted from the first storage control apparatus 10to the second storage control apparatus 20.

According to the above mechanism, even when the second storage controlapparatus 20 does not have the mechanism concerning check codes that thefirst storage control apparatus 10 has, the mechanism concerning checkcodes can be applied to the data to be stored in the second logic volume21.

<Extension of Scope to Apply Commands>

The first storage control apparatus 10 has a mechanism for interpretingand executing commands which the second storage control apparatus 20does not support (hereinafter referred to as “specific commands”). Thefirst storage control apparatus 10 further has a mechanism for applyingthe specific commands also to the data stored in the second logic volume21 of the second storage control apparatus 20. This mechanism iseffective when, for example, the second storage control apparatus 20does not support the specific commands.

When the first storage control apparatus 10 has received from a hostcomputer a data input/output request targeting a storage device of thesecond storage control apparatus 20, the first storage control apparatus10 checks whether the command described in the data input/output requestis a specific command or not. Then, if the command is a specificcommand, the first storage control apparatus 10 creates a command, whichthe second storage control apparatus 20 can interpret and execute, forallowing the second storage control apparatus 20 to execute a processfor responding the command and transmits to the second storage controlapparatus 20 a data input/output request in which the created command isdescribed. That is, the first storage control apparatus 10 functions ina sense as a command converting apparatus that converts the specificcommands that the second storage control apparatus 20 cannot interpretand execute into commands that the second storage control apparatus 20can interpret and execute.

Since the first storage control apparatus 10 functions as a commandconverting apparatus for the second storage control apparatus 20 in thismanner, even when the second storage control apparatus 20 does not haveany intelligent functions, the host computer can utilize the storageresources of the second storage control apparatus 20 as if the secondstorage control apparatus 20 has such functions (or as if the firststorage control apparatus 10 is integrated with the second storagecontrol apparatus 20).

Furthermore, the scope to apply commands that only the first storagecontrol apparatus 10 can interpret and execute can be extended to thesecond storage control apparatus 20. Therefore, when, for example, thefirst storage control apparatus 10 is introduced to an environment wherethe second storage control apparatus 20 is installed, while theextension of storage resource is being progressed by a storage device ofthe second storage control apparatus 20 being an existing asset, thecommands which only the first storage control apparatus 10 can interpretand execute can be applied when the storage resource of the secondstorage control apparatus 20 is utilized and, for example, in a datacenter etc., the second storage control apparatus 20 being an existingasset can be effectively utilized.

A structure for realizing the above mechanisms will be described indetail.

FIG. 19 shows the hardware structure of the first storage controlapparatus 10 and the second storage control apparatus 20 used in thefollowing description and FIG. 20 shows the main functional blocks thatthe first storage control apparatus 10 and the second storage controlapparatus 20 have and that are realized by the hardware shown in FIG. 19and the software being run on that hardware. However, a storageapparatus 60 is omitted in FIG. 20.

(1) Specific Reservation Command

A case where the specific commands are specific reservation commandsdefined in SCSI standard will be described as an example. In addition tothe conventional reservation command function conforming to the SCSIstandard, for each LU, setting such as write-in enable/unable, read-outenable/unable etc. for each WWN (World Wide Name) (for example, a WWNgiven to the host computer 30) attached to a data input/output requestcan be carried out to the specific reservation commands.

FIG. 21 illustrates a situation where an LUN of the second storagecontrol apparatus 20 is managed by being mapped on the first storagecontrol apparatus 10. In this figure, the storage apparatus 60 isomitted. As to the detailed mapping method, since it is same as the onedescribed above with FIG. 2 and its description is omitted.

FIG. 22 illustrates an operation when a data input/output request inwhich a specific reservation command targeting a storage device of thesecond storage control apparatus 20 is described is transmitted from ahost computer 31 to the first storage control apparatus 10. In thisfigure, the storage apparatus 60 is omitted.

A specific reservation command is transmitted from the first hostcomputer 31 to the first storage control apparatus 10 and the firststorage control apparatus 10 receives the command (S2211). The specificreservation command received by the first storage control apparatus 10is referred to the LU map information table 2300 shown in FIG. 23 by acommand analysis/execution unit 1011 of the first storage controlapparatus 10. Therefore, the command analysis/execution unit 1011recognizes that an LU being set in the command targets the storagedevice of the second storage control apparatus 20 (S2212), sets (i.e.,reservation) the reservation flag of the LU in the reservationinformation table 2400 shown in FIG. 24 and simultaneously registers theWWN of the host computer 31 that has transmitted the data input/outputrequest in the reservation information table 2400 relating the WWN toits LU (S2213).

Next, a data input/output request in which a data write-in command(“Write” command) is described is transmitted from the first hostcomputer 31 to the first storage control apparatus 10 and the firststorage control apparatus 10 receives it (S2214). Then, the commandanalysis/execution unit 1011 checks whether the WWN described in thereceived data input/output request is same as the WWN registered in thereservation information table 2400 as to the LU being the target of thedata input/output request (S2215). In this case, the WWNs match and thecommand analysis/execution unit 1011 progresses the process for the datawrite-in command.

Next, the command analysis/execution unit 1011 instructs thedata-caching unit 1013 to store in the cache memory 13 (not shown inFIG. 22) the data of write-in target received attached to the datawrite-in command (S2216) and the data-caching unit 1013 stores in thecache memory 13 the data of write-in target and notifies to a remote I/Ocontrol unit 1012 that it has stored the data (S2217).

Next, the command analysis/execution unit 1011 controls the remote I/Ocontrol unit 1012 (S2218) and the remote I/O control unit 1012 transmitsto the second storage control apparatus 20 the data write-in commandabout the write-in data stored in the cache memory 13 (S2219). At thisstage, the data write-in command is a command conforming to the SCSIstandard that the second storage control apparatus 20 also can analyzeand execute.

The data write-in command received by the second storage controlapparatus 20 is analyzed in the command analysis/execution unit 2011 ofthe second storage control apparatus 20 and the data caching unit 2013stores in the cache memory (not shown) the data of write-in targetreceived with the data write-in command (S2220). Then, the diskinput/output control unit 19 stores in the storage device (not shown)the data of write-in target stored in the cache memory of the secondstorage control apparatus 20.

On the other hand, when a data input/output request in which a commandtargeting an LU during reservation is described has been transmittedfrom a computer other than the first host computer 31, for example, asecond host computer 32 to the first storage control apparatus 10(S2231), the command analysis/execution unit 1011 of the first storagecontrol apparatus 10 checks whether the WWN described in the receiveddata input/output request is same as the WWN registered in thereservation information table 2400 for the LU being the target of thedata input/output request (S2232). At this stage, in this case, sincethe WWNs are not same, the command analysis/execution unit 2011transmits to the second host computer 32 a message telling that the LUis in reservation (S2233).

According to the above mechanism, the scope to apply the specificreservation commands that only the first storage control apparatus 10can interpret/execute can be extended to the second storage controlapparatus 20. Therefore, when, for example, the second storage controlapparatus 20 having no function for interpreting/executing the specificcommands is installed and the first storage control apparatus 10 havingsuch functions is introduced, while extension of the storage resource isbeing progressed by the storage device of the second storage controlapparatus 20 being an existing asset, the function for the specificreservation commands can be applied when the storage resource of thesecond storage control apparatus 20 is utilized. Therefore, the existingassets can be effectively utilized in, for example, data centers.

(2) E-Copy Command

Next, the case where the specific commands are extended copy commands(E-copy commands) defined in SCSI will be described. The commands areused when, for example, the device itself that has issued the commanddoes not copy the data but the copying is carried out between otherdevices.

FIG. 25 illustrates an operation of the storage system when an E-copycommand is transmitted from the first host computer 31 to the firststorage control apparatus 10 an E-copy command instructing to copy thedata in the second logic volume 21 of the second storage controlapparatus 20 to a back-up device 90 connected to a third storage controlapparatus 80.

First, an E-copy command is transmitted from the first host computer 31to the first storage control apparatus 10 and the first storage controlapparatus 10 receives this command. (S2511).

The E-copy command received by the first storage control apparatus 10 isreferred to the LU map information table 2300 shown in FIG. 23 by thecommand analysis/execution unit 1011 of the first storage controlapparatus 10. As a result of this, the command analysis/execution unit1011 recognizes that the logic volume being the copy target designatedin the command is targeting the second logic volume 21 of the secondstorage control apparatus 20 (S2512). The command analysis/executionunit 1011 also stores in a command control buffer 1015 on the controlmemory 14 a source address being the address of the copy source device(the second logic volume) set in the command and a destination addressbeing the address of copy destination device (the back-up device 90)(S2513).

Next, the command analysis/execution unit 1011 instructs the remote I/Oexecution unit 1012 to transmit a data read-out command to the secondstorage control apparatus 20 organizing the second logic volume 21designated by the source address (S2514). Then, the remote I/O executionunit 1012 having received this instruction transmits to the secondstorage control apparatus 20 a data read command being a commandconforming to SCSI standard that can be analyzed/executed in the secondstorage control apparatus 20 (S2515).

When the second storage control apparatus 20 has received the data readcommand, the command analysis/execution unit 2011 of the second storagecontrol apparatus 20 analyzes this command, reads out the targeted databy instructing the disk input/output control unit 19 to do so (S2516)and transmits the data to the first storage control apparatus 10(S2517). This read-out process is executed utilizing the data in thecache memory of the second storage control apparatus 20 if the dataexists there. If the data does not exist there, the disk input/outputcontrol unit 19 reads out the data from the second logic volume 21 andstores it in the cache memory and the read-out is executed utilizing thedata in the cache memory.

Next, when the remote I/O execution unit 1012 of the first storagecontrol apparatus 10 has received data transmitted from the secondstorage control apparatus 20, the remote I/O execution unit 1012notifies the data caching unit 1013 accordingly (S2518). The datacaching unit 1013 having received this notice stores the data in thecache memory 13 and notifies the command analysis/execution unit 1011that it has stored the data (S2519).

Next, the command analysis/execution unit 1011 having received thisnotice notifies the remote I/O execution unit 1012 that it will transmitthe data and a data write-in command about the data to the third storagecontrol apparatus 80 connected to the back-up device 90 designated by adestination address (S2520). The remote I/O execution unit 1012 havingreceived this notice transmits to the third storage control apparatus 80the data and a data write-in command (S2521). Then, when the thirdstorage control apparatus 80 has received the data and the data write-incommand, it controls the back-up device 90 and starts writing the datain a storage medium (S2522). As the back-up device 90, there are, forexample, a disk drive, a DAT tape drive, DVD-RAM, MO, CD-R, cassettetape etc.

According to the above mechanism, the scope to apply the E-copy commandsthat only the first storage control apparatus 10 can interpret/executecan be extended to the second storage control apparatus 20. Therefore,when, for example, the second storage control apparatus 20 having nofunction for interpreting the E-copy commands is installed and the firststorage control apparatus 10 having that function is introduced, whileextension of the storage resource is being progressed by the storagedevice of the second storage control apparatus 20, the function for theE-copy commands can be applied when the storage resource of the secondstorage control apparatus 20 is utilized. Therefore, the old storagecontrol apparatus can be effectively utilized.

<Details of Information Collection Function>

Next, the details of the above-described information collection functionwill be described. This function is executed taking the opportunitiessuch as, for example, when the first storage control apparatus 10 isintroduced newly to the storage system, when the structure of anotherapparatus has been changed and when start-up direction has been issuedby a user.

FIG. 26 shows a flowchart illustrating processes executed by the firststorage control apparatus 10 when this function is executed. In thisprocess, the first storage control apparatus 10, first, transmits to allthe ports accessible on the second network 51, for example, a port IDand an “Inquiry” command conforming to the SCSI standard designating anLUN of a device connected to each port and, as a result of this, obtainsthe structure of another apparatus as a candidate for the second storagecontrol apparatus 20 (S2611 and S2612). The first storage controlapparatus 10 judges whether the apparatus can be utilized as the secondstorage control apparatus 20 or not based on the information obtained bythe command such as the name and the type of the apparatus. For thejudgment, the first storage control apparatus 10 keeps storing in thecontrol memory 14 etc. the relation between names and types ofapparatuses and determinations whether they can be used as the secondstorage control apparatus 20 or not.

In the above judgment, when the first storage control apparatus 10 hasfound an apparatus that can be used as the second storage controlapparatus 20, it transmits to the apparatus a “Read Capacity” commandconforming to the SCSI standard following the “Inquiry” command (S2613).Therefore, information provided by the apparatus such as storagecapacity can be obtained. The first storage control apparatus 10 storesin the structure information management table 41 the informationobtained in this manner (S2614).

<Route Dynamic Selection Function>

In this storage system, the first storage control apparatus 10 has afunction for dynamically select the data transmission route between thefirst storage control apparatus 10 and the second storage controlapparatus 20. This function will be described in detail in this section.

First, the mechanism for collecting information concerning the secondnetwork 51, that the first storage control apparatus 10 needs for thisdynamic selection function will be described. First, the first storagecontrol apparatus 10 obtains the information concerning the network fromrelay apparatuses such as, for example, Fiber Channel switches on thesecond network 51 and stores the information in the control memory 14.The information concerning the network is network topology informationand node information in the network conforming to the Fiber Channelstandard, the SCSI standard or the iSCSI standard. This information isstored in devices such as switches constituting the network.

When, for example, a plurality of network routes for reaching the secondstorage control apparatus 20, the first storage control apparatus 10,based on the information collected as above, selects one of the routesor selects different routes to a plurality of ports for the purpose ofload distribution, and instructs the network to set the route(s). Atthis stage, the first storage control apparatus 10 selects dynamicallythe optimal network route(s) considering the congestion on the networkand access status to the second storage control apparatus 20. When ithas been confirmed by checking the access status of the network that theselected route(s) is/are interrupted by obstacle(s), a dynamic routecontrol is executed in which the route(s) is/are automatically switched.

Furthermore, the first storage control apparatus 10 changes the zoningsetting for the purpose of improving security etc., dynamically selectsthe route(s) such that the interference with other apparatuses existingon the second network 51 is suppressed and selects automatically onlythe route(s) being permitted to access in association with theabove-described access limit function.

Other Embodiments

A storage system and a method for controlling the storage systemaccording to the invention has been described based on embodiments.However, the above-described embodiments of the invention onlyfacilitates the understanding of the invention and is not intended tolimit the invention. The invention can be changed and improved withoutdeparting from the scope and the spirit of the invention and includesits equivalents.

In the above description, the first network 50 and the second network 51can be connected to each other or each of them can be independent.

It can be structured such that a plurality of second storage controlapparatus 20 exist for one first storage control apparatus 10.

In the above description, the first storage control apparatus 10 and thesecond storage control apparatus 20 are described as disk arrayapparatuses, however, they are not limited to disk array apparatuses andcan be, for example, semiconductor disk apparatuses using semiconductormemories as storage devices.

The storage system can be structured such that the first and the secondstorage control apparatus 10 and 20 are connected through acommunication line conforming to the SCSI standard.

According to the invention, it is possible to effectively utilize theold storage control apparatuses when, for example, a storage controlapparatus has been newly introduced to an existing storage system.

While illustrative and presently preferred embodiments of the presentinvention have been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

1-48. (canceled)
 49. A method for controlling a storage system includinga host computer, and a first and a second storage control apparatuseseach having a function for receiving a data input/output requesttransmitted from said host computer and executing a data input/outputprocess for a storage device in response to said data input/outputrequest received, comprising: connecting a first communication pathbetween said host computer and said first storage control apparatus toeach other; connecting a second communication path between said firststorage control apparatus and said second storage control apparatus toeach other; collecting information concerning a storage device for whichsaid second storage control apparatus executes data input/outputprocesses; storing in said first storage control apparatus saidinformation concerning said storage device; receiving by said firststorage control apparatus a first data input/output request transmittedfrom said host computer through said first communication path; when saidfirst storage control apparatus has judged that said first datainput/output request is not to be handled by said first storage controlapparatus based on said information concerning said storage device thatsaid first storage control apparatus stores, transmitting by said firststorage control apparatus a second data input/output requestcorresponding to said first data input/output request, to said secondstorage control apparatus through said second communication path; and bysaid second storage control apparatus, receiving said second datainput/output request and executing a data input/output processcorresponding to said second data input/output request received.
 50. Amethod for controlling a storage system according to claim 49, whereinsaid information concerning said storage device include at least one ofmanagement information of storage areas for one or more logic volume(s)organized on a storage area provided by said storage device, informationconcerning performance of said logic volume(s), information concerningstorage capacities of said logic volume(s), and information concerningthe remaining capacities of said logic volume(s).
 51. A method forcontrolling a storage system according to claim 49, wherein said seconddata input/output request conforms to the same data format as a dataformat of the data input/output request that said second storage controlapparatus is configured to receive directly from said host computer. 52.A method for controlling a storage system according to claim 49, whereinsaid second data input/output request is transmitted and received inconformity with the same protocol as a protocol used when said secondstorage control apparatus makes direct transmission to and directreception from said host computer.
 53. A method for controlling astorage system including a host computer, and a first and a secondstorage control apparatuses each having a function for receiving a datainput/output request transmitted from said host computer, executing adata input/output process for a storage device in response to said datainput/output request received, and organizing a plurality of logicvolumes on a storage area provided by said storage device for which saidfirst and said second storage control apparatuses execute respectivedata input/output processes, comprising: connecting a firstcommunication path between said host computer and said first storagecontrol apparatus to each other; connecting a second communication pathbetween said first storage control apparatus and said second storagecontrol apparatus to each other; collecting information concerning astorage device for which said second storage control apparatus executesdata input/output processes; storing in said first storage controlapparatus said information concerning said storage device; transmittingby said host computer a first data input/output request directed to alogical volume which is one of said plurality of logic volumes and atarget of data input/output processes executed by said second storagecontrol apparatus; receiving by said first storage control apparatussaid first data input/output request directed to said logical volume; bysaid first storage control apparatus, judging that said first datainput/output request is not to be handled by said first storage controlapparatus based on said information concerning said storage device thatsaid first storage control apparatus stores; transmitting by said firststorage control apparatus a second data input/output requestcorresponding to said first data input/output request, to said secondstorage control apparatus through said second communication path; and bysaid second storage control apparatus, receiving said second datainput/output request and executing a data input/output processcorresponding to said second data input/output request received.